14,836 research outputs found
Energy absorption by "sparse" systems: beyond linear response theory
The analysis of the response to driving in the case of weakly chaotic or
weakly interacting systems should go beyond linear response theory. Due to the
"sparsity" of the perturbation matrix, a resistor network picture of
transitions between energy levels is essential. The Kubo formula is modified,
replacing the "algebraic" average over the squared matrix elements by a
"resistor network" average. Consequently the response becomes semi-linear
rather than linear. Some novel results have been obtained in the context of two
prototype problems: the heating rate of particles in Billiards with vibrating
walls; and the Ohmic Joule conductance of mesoscopic rings driven by
electromotive force. Respectively, the obtained results are contrasted with the
"Wall formula" and the "Drude formula".Comment: 8 pages, 7 figures, short pedagogical review. Proceedings of FQMT
conference (Prague, 2011). Ref correcte
The Quantum-Classical Crossover in the Adiabatic Response of Chaotic Systems
The autocorrelation function of the force acting on a slow classical system,
resulting from interaction with a fast quantum system is calculated following
Berry-Robbins and Jarzynski within the leading order correction to the
adiabatic approximation. The time integral of the autocorrelation function is
proportional to the rate of dissipation. The fast quantum system is assumed to
be chaotic in the classical limit for each configuration of the slow system. An
analytic formula is obtained for the finite time integral of the correlation
function, in the framework of random matrix theory (RMT), for a specific
dependence on the adiabatically varying parameter. Extension to a wider class
of RMT models is discussed. For the Gaussian unitary and symplectic ensembles
for long times the time integral of the correlation function vanishes or falls
off as a Gaussian with a characteristic time that is proportional to the
Heisenberg time, depending on the details of the model. The fall off is
inversely proportional to time for the Gaussian orthogonal ensemble. The
correlation function is found to be dominated by the nearest neighbor level
spacings. It was calculated for a variety of nearest neighbor level spacing
distributions, including ones that do not originate from RMT ensembles. The
various approximate formulas obtained are tested numerically in RMT. The
results shed light on the quantum to classical crossover for chaotic systems.
The implications on the possibility to experimentally observe deterministic
friction are discussed.Comment: 26 pages, including 6 figure
Cryptic Torrent Frogs of Myanmar: An Examination of the Amolops marmoratus Species Complex with the Resurrection of Amolops afghanus and the identification of a New Species
Cataloged from PDF version of article.We investigated diversity in the Amolops marmoratus species complex within Myanmar using both molecular and morphological characters from recently collected specimens. Based on congruence between multivariate analyses of quantitative morphological characters and phylogenetic analyses of nucleotide variation in the 16S ribosomal gene conducted on 43 out of 182 frogs examined, we recognize A. marmoratus for specimens from the states of Mon and Shan and northern Tanintharyi Division and designate a neotype for this species; resurrect A. afghanus (Gnther, 1858) from synonymy with A. marmoratus for specimens from the northern state of Kachin and designate a lectotype for this species; recognize A. panhai for specimens from Tanintharyi, a new country record; and describe a new species for specimens from the western states of Chin and Rakhine, and Sagaing Division. © 2012 by the American Society of Ichthyologists and Herpetologists
Quantum dissipation due to the interaction with chaotic degrees-of-freedom and the correspondence principle
Both in atomic physics and in mesoscopic physics it is sometimes interesting
to consider the energy time-dependence of a parametrically-driven chaotic
system. We assume an Hamiltonian where . The
velocity is slow in the classical sense but not necessarily in the
quantum-mechanical sense. The crossover (in time) from ballistic to diffusive
energy-spreading is studied. The associated irreversible growth of the average
energy has the meaning of dissipation. It is found that a dimensionless
velocity determines the nature of the dynamics, and controls the route
towards quantal-classical correspondence (QCC). A perturbative regime and a
non-perturbative semiclassical regime are distinguished.Comment: 4 pages, clear presentation of the main poin
The potential of the ground state of NaRb
The X state of NaRb was studied by Fourier transform
spectroscopy. An accurate potential energy curve was derived from more than
8800 transitions in isotopomers NaRb and NaRb. This
potential reproduces the experimental observations within their uncertainties
of 0.003 \rcm to 0.007 \rcm. The outer classical turning point of the last
observed energy level (, ) lies at \AA, leading
to a energy of 4.5 \rcm below the ground state asymptote.Comment: 8 pages, 6 figures and 2 table
The shape of invasion perclation clusters in random and correlated media
The shape of two-dimensional invasion percolation clusters are studied
numerically for both non-trapping (NTIP) and trapping (TIP) invasion
percolation processes. Two different anisotropy quantifiers, the anisotropy
parameter and the asphericity are used for probing the degree of anisotropy of
clusters. We observe that in spite of the difference in scaling properties of
NTIP and TIP, there is no difference in the values of anisotropy quantifiers of
these processes. Furthermore, we find that in completely random media, the
invasion percolation clusters are on average slightly less isotropic than
standard percolation clusters. Introducing isotropic long-range correlations
into the media reduces the isotropy of the invasion percolation clusters. The
effect is more pronounced for the case of persisting long-range correlations.
The implication of boundary conditions on the shape of clusters is another
subject of interest. Compared to the case of free boundary conditions, IP
clusters of conventional rectangular geometry turn out to be more isotropic.
Moreover, we see that in conventional rectangular geometry the NTIP clusters
are more isotropic than TIP clusters
Smoothed universal correlations in the two-dimensional Anderson model
We report on calculations of smoothed spectral correlations in the
two-dimensional Anderson model for weak disorder. As pointed out in (M.
Wilkinson, J. Phys. A: Math. Gen. 21, 1173 (1988)), an analysis of the
smoothing dependence of the correlation functions provides a sensitive means of
establishing consistency with random matrix theory. We use a semiclassical
approach to describe these fluctuations and offer a detailed comparison between
numerical and analytical calculations for an exhaustive set of two-point
correlation functions. We consider parametric correlation functions with an
external Aharonov-Bohm flux as a parameter and discuss two cases, namely broken
time-reversal invariance and partial breaking of time-reversal invariance.
Three types of correlation functions are considered: density-of-states,
velocity and matrix element correlation functions. For the values of smoothing
parameter close to the mean level spacing the semiclassical expressions and the
numerical results agree quite well in the whole range of the magnetic flux.Comment: 12 pages, 14 figures submitted to Phys. Rev.
Oxygen Moment Formation and Canting in Li2CuO2
The possibilities of oxygen moment formation and canting in the quasi-1D
cuprate Li2CuO2 are investigated using single crystal neutron diffraction at 2
K. The observed magnetic intensities could not be explained without the
inclusion of a large ordered oxygen moment of 0.11(1) Bohr magnetons.
Least-squares refinement of the magnetic structure of Li2CuO2 in combination
with a spin-density Patterson analysis shows that the magnetization densities
of the Cu and O atoms are highly aspherical, forming quasi-1D ribbons of
localised Cu and O moments. Magnetic structure refinements and low-field
magnetization measurements both suggest that the magnetic structure of Li2CuO2
at 2 K may be canted. A possible model for the canted configuration is
proposed.Comment: 10 pages, 8 figures (screen resolution
Faith framing climate: a review of faith actors’ definitions and usage of climate change
Faith actors shape understandings of what climate change is and what responses ought to be pursued at local and global levels and in civil society and policy arenas alike. As an issue which can be described and responded to in multiple and varied ways and given faith actors’ role and influence in local and global civil society, this article aims to provide a better understanding of the ways in which faith actors use framings of climate change. Framing is taken to be a broad notion encompassing the ways climate change is defined by faith actors and how it becomes embedded into the language of their faith, operational structures, and development work. Drawing on an analysis of data collected from the websites of 50 faith actors, we found that 45 situated climate change within moral and religious frameworks and 41 emphasized the effects on and effects of humans. Climate change is taken to be a moral and socio-political issue, and by 18 as a justice issue, on which humans have an imperative to act. Despite their diversity, the results indicate a distinctively faith-based ability to situate climate change in moral and religious frameworks whilst remaining connected to the practical effects thereof
Collective versus single-particle effects in the optical spectra of finite electronic quantum systems
We study optical spectra of finite electronic quantum systems at frequencies
smaller than the plasma frequency using a quasi-classical approach. This
approach includes collective effects and enables us to analyze how the nature
of the (single-particle) electron dynamics influences the optical spectra in
finite electronic quantum systems. We derive an analytical expression for the
low-frequency absorption coefficient of electro-magnetic radiation in a finite
quantum system with ballistic electron dynamics and specular reflection at the
boundaries: a two-dimensional electron gas confined to a strip of width a (the
approach can be applied to systems of any shape and electron dynamics --
diffusive or ballistic, regular or irregular motion). By comparing with results
of numerical computations using the random-phase approximation we show that our
analytical approach provides a qualitative and quantitative understanding of
the optical spectrum.Comment: 4 pages, 3 figure
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